Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $198.61   5.661%   $209.8533   $209.85   $209.85   $209.90  
  Purchase #2 $134.97   5.475%   $142.3596   $142.36   $142.35   $142.40  
  Purchase #3 $173.77   8.827%   $189.1087   $189.11   $189.10   $189.10  
  Purchase #4 $232.48   4.263%   $242.3906   $242.39   $242.40   $242.40  
  Purchase #5 $111.53   7.428%   $119.8144   $119.81   $119.80   $119.80  
  Purchase #6 $112.66   3.292%   $116.3688   $116.37   $116.35   $116.40  
  Purchase #7 $155.79   4.871%   $163.3785   $163.38   $163.40   $163.40  
  7 purchase totals = $1,119.81       $1,183.2739   $1,183.27   $1,183.25   $1,183.40